Here's a much beloved VGC graph which gives some context to the PS3 spike.
Some states:
Number of weeks since launch 360 sold >500K = 13
Number of weeks since launch PS3 sold >500K = 5
Number of weeks since launch Wii sold >500K = 23
Million selling weeks: Only Wii = 8
Number of weeks outside holiday period (Nov - Jan) consoles sold > 500K = 5 (3 for Wii, 2 for PS3).
What happened to sales in those previous 4 instances of >500K sales outside holiday period? Wii: 736K-->393K (46% drop); 573K-->392K (32% drop); 515K-->368K (29% drop). PS3: 584K-->157K (73% drop). Average % drop for those 4 instances = 45% drop.
There is reason to believe (Slim sku + price reduction) that this time's PS3 week 2 sales drop will be more Wii-like than the one previous PS3 instance. So it seems to be reasonable to look for a 45% or less sales dip in the next sales chart.
Outside the holiday period >500K weeks are unusual, but not unheard of. They are rare enough that they don't amount to a significant change in the overall fortunes of a console.
The important thing for PS3 though is not sales spikes around launch events, but a significant lift in baseline sales.
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